Foot-operated controllers have traditionally been limited to pedals mechanically linked to valves, levers, regulators or the like, such as accelerator and brake pedals for automobiles, or pedals capable of generating only a single electrical signal, such as for controlling a sewing machine. These conventional foot-operated controllers are not practical for simultaneously controlling multiple functions in a more complicated device such as a prosthetic hand.
Annually, approximately 40,000 people in the United States either lose or are born without a limb. Approximately 12,000 of these cases involve an upper extremity. There are three general categories of upper extremity prosthesis. These include a passive, cosmetic prosthesis; a cable-driven body-powered prosthesis; and an externally powered prosthesis that is electrically controlled by either myoelectric sensors or specialized switches.
The cable-driven, body-powered, upper-limb prostheses have not changed significantly since development in the 1950s. These prostheses employ relatively old technology involving the use of a shoulder harness and steel cables for operation. The externally powered, electrically controlled prostheses have certain advantages over the cable-driven, body-powered prostheses, including superior pinch force (about 15–25 pounds as compared with 7–8 pounds); improved cosmetic and social acceptance; freedom from an uncomfortable harness; and improved function for high-level amputees. However, proponents of the more traditional cable-driven, body-powered prostheses claim that the cable-driven, body-powered prostheses are more functional and efficient because the reaction time to response is immediate, noise level is held to a minimum, and operation is more dependable and stable.
The conventional prostheses do not satisfy many of the basic needs of individuals who have either lost a limb or were born without a limb. In particular, there is a need for prosthetic devices that are lighter in weight, capable of operating all day (more than 12 hours) on a single charge, and provide the ability to drive an automobile without modification to the vehicle. Further, there is a desire for prosthetic devices which provide more function than existing devices, improved suspension and actuation, and improved gripping capabilities.
A tendon-activated, pneumatic controlled artificial hand having up to three independently functioning fingers has been developed. However, this device can only be used by individuals having a forearm and some phantom feeling (i.e., the sense that they can still feel their missing hand). It is believed that when this device is perfected, its users will be able to operate the artificial hand using muscles and muscle signals from the forearm. A computer will receive muscle signals from the forearm and transmit corresponding signals to the artificial hand to stimulate movement of the fingers.
A prosthetic limb has been developed that uses myolelectric signals to control a two-motor system. One motor operates to provide high torque at low speed, while a second motor provides low torque at high speed. Together, they accomplish reasonable torque and reasonable speed to provide simultaneous closure of the fingers against a fixed thumb, or simultaneous closure of the fingers and the thumb.
Another device uses a microprocessor to control grip force and finger/hand orientation of a prosthetic hand. This device uses two myoelectric inputs, including one for an extensor muscle, which when tensioned opens the hand wider, and one for a flexor muscle, which is used to switch the hand into a “hold” mode. The fingers curl continuously toward an opposed, moveable thumb. However, there is not any independent finger or wrist control.
A gloveless endoskeletal prosthetic hand has been developed having a multi-position passive thumb with four, three-jointed apposed fingers, which all move in unison. A harness cable control closes the fingers simultaneously, and the fingers extend upon relief of cable tension.
A prosthetic hand has been developed with co-contraction switching, where the wearer is able to switch control from the hand to the wrist by a quick twitch of the two control muscles. Control back to functions of the hand is restored by another quick twitch.
It is believed that there remains a need for a practical control device for generating a plurality of independent signals for controlling a plurality of functions in a prosthetic hand having a plurality of independently controllable fingers.